There is mobile IP as one of mobility managing methods in the Internet system. The mobile IPv4, corresponding to IPv4 (Internet Protocol Version 4), is standardized in RFC3220 (IP Mobility Support). Meanwhile, the mobile IPv6, corresponding to IPv6 (Internet Protocol Version 6), is now under standardization in the Internet draft draft-ietf-mobileip-ipv6 (Mobility Support in IPv6). These protocols enable communications by the use of the same address even where the mobile terminal roams between different networks.
In mobile IPv6, the mobile terminal, where distant from a home link, acquires the prefix information of a currently connected link from the network information sent from an access router of the currently connected link, thereby generating a care of address for use on that link. Thereafter, by sending a binding update message to a home agent, the care of address is registered as a primary care of address to a home agent on a home link of the mobile terminal. The home agent, after receiving the binding update message from the mobile terminal, creates or updates a binding cache to associate the home address and the care of address together.
The home agent makes reference to a binding cache and proxy-receives a packet sent destined for the home address on the home link of the mobile terminal, to encapsulate the proxy-received packet, thereby carrying out a process to transfer it to a care of address of the mobile terminal. The mobile terminal decapsulates the packet transferred by the home agent, thus receiving the packet destined for the home address of the mobile terminal.
Meanwhile, conventionally, as a mobile communication method of this field, there is something like a description in JP-T-2002-503415. FIG. 23 shows the conventional mobile communication method described in that publication.
In FIG. 23, a plurality of mobile communication networks are configured by private automatic branch exchanges (PABXs) 2303, home base stations (HBSs) 2305, digital enhanced cordless telecommunications (DECTs) 2306, and mobile terminals 2304. These mobile communication networks are connected by a mobile subscriber repeater (M-TVSt) 2301. A home data bank (HDB) 2302 acquires and manages a call number of the mobile terminal 2304 for use on each network through the private automatic branch exchange (PABX) 2303 on each mobile communication network, and associates it with a representative number, thereby making it possible to transfer an incoming call from the external.
However, in the mobile communication system using a conventional mobile IP, the mobile terminals and the home agents are in a one-to-one relationship, wherein the home agents are installed/controlled on each domain of mobile communication operator. In such a situation, the mobile terminal when moving between domains is assigned with a different home address by a moved-in domain. In the communications from the external, the external terminal is required to select a home address of accessible mobile terminal, i.e. to know an operator domain to which the mobile terminal is now getting access, which forcibly lowers communication efficiency and convenience.
Meanwhile, it is possible to support a change of home address by using a DNS for managing a correspondence of a host name and address of mobile terminal, particularly a dynamic DNS for dynamic update. However, it generally takes a time of several minutes or more from registration up to stabilizing the DNS system, thus involving many problems in swift responding to mobile terminal roaming.
Incidentally, in the foregoing publication, in a closed communication network for a mobile communication network such as GSM, association is provided by the home data bank (HDB) 2302 and the private automatic branch exchange (PABX) 2303 on each communication network. However, there is a problem of deficient flexibility in the Internet that is a freely distributed network including those mobile communication networks.